1. Field of the Invention
The present invention relates to a heat activation method of a thermosensitive adhesive label comprising a support, and a thermosensitive adhesive layer which is formed on the support without a liner (i.e., a disposable backing sheet) and is not adhesive at room temperature, so as to make the thermosensitive adhesive layer adhesive with the application of heat thereto. More particularly, the present invention relates to the heat activation method of the above-mentioned thermosensitive adhesive label, comprising the step of bringing the thermosensitive adhesive layer of the thermosensitive adhesive label into contact with a heating medium of which surface portion comprises a silicone resin.
In addition, the present invention also relates to an apparatus for heat-activating the above-mentioned thermosensitive adhesive layer of the thermosensitive adhesive label.
2. Discussion of Background
Recently, a recording label, in particular, a thermosensitive recording label has been used in a wide variety of fields, for example, in the system of point of sales (POS). The above-mentioned conventional thermosensitive recording label generally comprises a pressure-sensitive adhesive layer, and a liner (i.e., disposable backing sheet) which is attached to the adhesive layer.
Such a thermosensitive recording label is useful, but it has many shortcomings. For instance, a large space is required during the storage of the recording label because the liner thereof is relatively voluminous. Further, the step of releasing the liner from the pressure-sensitive adhesive layer is necessary when the thermosensitive recording label is used, and the liner must be discarded after released from the adhesive layer. Therefore, consideration must be given to the problem of waste disposal from the ecological viewpoint. In addition, the productivity and workability of the above-mentioned conventional thermosensitive adhesive label are poor, and the manufacturing cost is increased because of not only the cost of the linear itself, but also expenses involved by the treatment of the liner.
To solve the above-mentioned problems, there are proposed recording labels without a liner. For instance, as disclosed in Japanese Laid-Open Utility Model Applications 59-43979 and 59-46265 and Japanese Laid-Open Patent Application 60-54842, it is proposed to employ a pressure-sensitive adhesive in micro-capsule form in the adhesive layer, and to provide a releasing agent layer on a support, opposite to the side of a pressure-sensitive adhesive layer with respect to the support, in light of the storage. By the above-mentioned conventional proposals, however, the pressure-sensitive adhesive layer cannot be provided with sufficient adhesion, and it is impossible to print an image on the surface of the label, so that those proposals have not yet been put to practical use.
Furthermore, there is proposed a method of using a thermosensitive adhesive, as disclosed in Japanese Laid-Open Patent Application 63-303387 and Japanese Utility Model Publication 5-11573. When a recording label comprises a thermosensitive adhesive layer, heat-activation treatment of the thermosensitive adhesive layer becomes necessary. With respect to the above-mentioned heat activation treatment, the following methods are conventionally proposed: the application of hot air or infrared rays to the thermosensitive adhesive layer (Japanese Utility Model Publication 5-11573), the use of an electrical heater or induction coil (Japanese Laid-Open Patent Application 5-127598), the application of microwave to the thermosensitive adhesive layer (Japanese Laid-Open Patent Application 6-8977), the application of xenon flash to the thermosensitive adhesive layer (Japanese Laid-Open Patent Application 7-121108), and the application of halogen lamp to the thermosensitive adhesive layer (Japanese Laid-Open Patent Application 7-164750). Those heat activation methods have the advantages that the thermosensitive adhesive layer can be prevented from sticking to each heating medium because the thermosensitive adhesive layer can be activated without coming in direct contact with the heating medium in any of the above-mentioned heat activation methods. On the other hand, those heat activation methods have the drawback that it is necessary to add a light-absorbing material to the thermosensitive adhesive layer of the label. Further, the conventional apparatuses for heat-activating the thermosensitive adhesive layer of the label are not satisfactory in practical use in terms of safety, workability, size and cost.
In addition, when the above-mentioned thermosensitive adhesive label further comprises a thermosensitive coloring layer, it is required to prevent the coloring phenomenon in the background of the thermosensitive coloring layer during the heat activation process of the adhesive layer, so that it is extremely difficult to put this kind of thermosensitive adhesive label to practical use.
There is also proposed a heat activation method of the thermosensitive adhesive layer by bringing the thermosensitive adhesive layer into contact with a heating medium. For example, a heat-application drum and a heat-application roll serving as the above-mentioned heating media are respectively disclosed in Japanese Laid-Open Patent Applications 60-45132 and 6-263128. According to the above proposals, the surface portion of the above-mentioned heating media comprises Teflon.
In the case where the obtained adhesion of the thermosensitive adhesive layer is not strong, the thermosensitive adhesive layer can be prevented from transferring to the surface portion of the heating medium because a material with high releasability, such as Teflon, is used for the surface portion of the heating medium. However, when a thermosensitive adhesive layer is completely or continuously heat-activated so as to impart strong adhesion to the thermosensitive adhesive layer by the above-mentioned conventional heat activation methods, the heat-activated adhesive will transfer to the contact surface portion of the heating medium.
At present, there is no liner-less thermosensitive adhesive label that can match the conventional thermosensitive adhesive label equipped with a liner in the obtained adhesion of the thermosensitive adhesive layer and matching properties with the heat-activating apparatus.